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Due to the weather-related planting delays, some soybean fields will probably be tilled and planted this spring when the soil is too wet. This situation weakens the stability of soil aggregates and increases the potential for a crust to develop at the soil surface. A soil crust forms when rain drops strike soil aggregates, breaking them into individual sand, silt and clay particles. Once the particles are separated, they move with the water and pack together very tightly. As the soil dries, the closely-packed soil particles form a crust sealing the soil. A soil crust is more likely to develop on fine-textured soils, soils low in organic matter and tilled fields where surface residue levels are not sufficient to protect the soil aggregates from raindrop impact. Soil crusting reduces soybean emergence, oxygen diffusion and water infiltration and increases soil erosion.
Producers should identify which fields are most likely to form a crust and develop strategies for improving soybean emergence in these fields. One possible option is to plant your smallest soybean seed in fields prone to crusting. The smaller seed produces smaller cotyledons (seed leaves) that are more easily lifted out of the soil than the cotyledons of large-seeded soybeans. Another option is to plant these fields in 28- or 30-inch rows. The seeds are usually spaced closely enough within the row at these row widths to crack the crust and help each other emerge. Consider planting slightly shallower and lifting row cleaners to maintain residue cover over the row and improve emergence.
If heavy rainfall occurs within a few days after planting, look for signs of soil crusting after the soil dries and be prepared to use a rotary hoe to break the crust if rain is not predicted. If the crust is not broken up on a timely basis, the soybean seedlings will exhaust all of their energy reserves trapped beneath the crust, undergo mechanical damage such as broken hypocotyls and lost cotyledons while struggling to emerge or be invaded by plant pathogens.
A rotary hoe operated timely and correctly will break up an existing soil crust and improve soybean emergence without causing significant stand loss or excessive damage to the seedlings. Stop periodically and check the seedlings for mechanical damage. Crop damage can be reduced by operating the rotary hoe in the same direction as the rows and during the heat of the day when plants are less brittle. It may be necessary to reduce the operating speed if crop damage is unacceptable, and always avoid rotary hoeing during the vulnerable “crook stage.” Stand loss and crop injury can also be minimized by operating the rotary hoe just deep enough to breakup the crust.
The short-term effects of soil crusting can be reduced with proactive and remedial management practices this spring. The long-term solution is to increase soil organic matter levels and leave more crop residue on the soil surface.
Source: Michigan State University Extension
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